Signal reception



June 24, 1930. D. A. GRIFFIN 1 5 IGNAL RECEPTION Filed Aug. 1, 1923 hue/77b): 04/74 4. GF/ffl'n by A7714 patented June 24, 1930 UNITED. STATES DANA A. GRHFIN, E SUMMIT, NEW JERSEY, essreiqon '10 WESTERN ELEoTRro COM- PANY, INCORPORATED, 013 NEW YORK, N. Y., A CoEPOEA'rION OF EW YORK V SIGNAL RECEPTION Application'filed August 1, 1923. Serial No. 654,990.

The present invention relates to wave re-v ception, and particularly to the reception of high frequency waves such as radio waves. The invention has special application to radio frequency amplifiers. V g 7 It is an object of the invention to secure uniform and high amplification over a wide range of wave lengths in the relatively short Wave-length region. I

On account of the high capacity effects at the radio frequencies, it is much more difficult to obtain high amplification of radio frequency waves than of audio frequency'waves. These capacity efiects introduce substantial losses so that the efficiency of the amplifier is reduced, and they also produce resonance effects which tend to distort the wave being amplified and to give amplification peaks at certain frequencies and low amplification at other frequencies. 7

To secure high amplification it is preferred to use transformers between the various stages, although the invention, as will be seen, is not limited to any particular type of interstage circuit. It has been found that where transformers are used as interstage coupling, the frequency characteristic of the amplifier as a whole can be controlled appreciably by design of the transformers. This may be done, for example, by taking account of the internal tube-capacities with which the transformers are to cooperate and by varying the ratio of turns, the actual number of turns, the style of winding, the spacing between windings, and other dimensions to make the transformers give a less marked resonance effect at the portion of theamplifier characteristic where a peak occurs. Frequently this can onlybe done by a cut-andtry meth' od, as is well known by workers inthe art. In general this method maybe applied torany radio frequency amplifier and the frequency characteristic can beimproved up to a certain limit. The best that has been obtained heretofore by this method so far asapplicant is aware, is a fairly gradual change of amplification withwave length from no amplification (at the shortest wave length) through degrees of increasing amplification as the wave lengths increase, followed by decreas ing amplification with still longer waves until the point of no amplification is reached (at the longest Wave-lengths). In the wave length range of 200 to 1000 meters, the best that has heretofore been obtained, so far as applicant is aware, for a substantial amplification, is about a 2: 1 wave length ratio for example a range of 300 meters to about 600 meters, or a range of 250 meters to 500 meters.- A feature of applicants invention is the use of a balanced or push-pull tube circuit in one of the stages of a radio frequency amplifier, preferably the first stage. V

A. related feature is the use of coupling circuits of difierent frequency characteristics between the respective push-pull tubes and the succeeding stage. i Q

These features possess a numberof advantages, It is known that a radio-frequency amplifier can be stabilized and to a large extentbe prevented from singing by connecting the incoming circuit to the grid and cathode and to theplate through a small condenser,1that matches the grid-to-plate capacity of the tube, to render the amplifier circuit symmetrical. If a loop receiver is used, a center tapfrom the loop inductance is c011- nected to the cathode, and the other terminals are connected one to the grid and the other to the balancing condenser. 'Such a connection is disclosed andclaimed in U. S.- Patent No. 1,678,l88 granted to; Harald T. Friis July 24, 1928.: In the. push-pull tube circuit of the present invention, each tube balances theother so that the singing tendency is reduced in a manner closely analagous to the action of the balancing condenser.

Further, as stated in the Friis application the directional selectivity of theloop is increased by grounding its mid-point. This advantage is present in the circuit of the invention and there is the addedadvantage that the entire voltage generated in the loop is utilized in this invention instead of only halfthe loopvoltage as is usually the case.

A more important advantage, however, is that applicant is enabledto increase the wavelengthrange over which fairly uniform 'amplification may be carried; out and'at the same timeto increase the degree of amplification through this range. This is due to the fact that each tube with its separate connection to the loop and with its individual output characteristics maybe made to supplement the other so that the individual characteristics are added bothas to wave length range and amplitude. This results in a more fiat-tpped characteristic than has heretofore been obtained. That is, where the characteristics as pointed out above, have heretofore had a Varying amplification throughout their wave-length range, the invention provides substantially uniform amplification throughout a wave length range of well over a 2: 1 ratio and a gradually changing amplification each side of the uniform amplification range, so that a wavelength ratio o-f l or to 1 which is satisfactory for most purposes is obtained (for example 200 to 800 meters).

In addition to the primary purpose of the invention of securing improved radio-frequency amplification, the invention has a further marked advantage when applied to the so-called reflex type of circuit, in whichthe same tubes serve for radio and audio amplification. By so connecting the stages that the push-pull circuit forms the final stage'for the audio amplification, the quality of the signal is improved for the same volume, or the same quality can be maintained for a much larger output, than in the case of a single tube circuit.

The actual form of circuit which the invention may take is indicated by the tWo examples illustrated in the drawing, Fig. 1 being a schematic diagram of a radio frequency amplifier and detector, and Fig. 2 being a similar representation of a reflex circuit. Fig. 3 shows the manner of connecting a loop receiver to the circuit of Fig. 1. v i

In Fig. l the'tubes 1 and 2 are connected in balanced or push-pull relation and comprise the first stage of radio frequency am i plification. The tube?) has its input or grid circuit connected to the output circuits of both tubes 1 and 2. The waves thus amplified are detected by the tube 4: and the signal may be reproduced in any desired type of receiver such as the head set 5., p I

v The filaments of the first 0rpush-pull stage, and the filament of the second stage,

are heated from'battery 6, which is grounded through resistance '7 Since it maybe desirable to usea difierent type of tube at 4:, a separate battery is indicated for heating its filament. The'midpointof the secondary8 is grounded and the terminals of the winding are connected to'the grids of tubes 1'and'2. Tuning condenser 9 is connected across this winding to enable tuning to the received wave frequency. Space 'currentfor all of the tubes is supplied'from source 14:. I

' The transformers lO'12 and' 1113' for Coupling the push-pull stage to thesecond stagemay be designed to have different fretransformers were used in conjunction with 7 tubes of small internal capacity. These values are of course given for illustrative purposes only and are'not to be construed as limiting the invention; The number of turns determines the inductanceand the spacing and dimensioning control the capacity efi'ects of the coils and-to some extent the inductance as is well known. By thus varying the individual transformer" they maybe made to have overlapping frequency transmission characteristics to increase the total wave length range of the set, andthe manner of overlap may also be controlled to givea fairly uniform amplification over-a much greater wavelength range than the case with only a single tube stage and single transformer.

Since the tube'Q is a duplicate of tube 1, each serves to balance the capacity of the other with respect-to potentials tending to react on the grids, so that the singing -tendency is efiectively eliminated. V Instead of using an open aerial as shown, the loop aerial of 3 may housed byconnecting the similarlylettered contacts to each other and by opening switches 15" and 17 i Fig. 2 differs from l in that the audiofrequency transformers 18, 19 and 20 have been added to permit amplification of the detected signal by the same tubes 1, 2 and 3 that serve for radio frequency amplification. The detected signal is. fed from tube to the primary of repeating coil 18, the secondary of which is connected in th gridcircuitcf tube 3. The output of tub includes the primary of repeating coil so that the amplified signal is applied to the secondaries" of transformers 20 and to the gridseoftubes 1 and 2. If the tubes 1 and 2 are to actin push-pull relation for (the audio. frequency waves the direction windi of the secondaries of repeating coil 20 a d themanner of connection to the respective grids must be i i V primary windings of theinput transformer,v

'20 and of the secondary windings of the outi3oput transformer 19 are lettered to indicate the direction of winding, a-bcd being the series aiding connection. The condensers 21 to 25 are by-pass condensers for the radiofrequency waves, around the audio-frequency transformer-windings.

A loud-speaking receiver may be used at 5, and may be fed with large power since the stage 1, 2, which is the most heavily loaded stage at audio-frequency and the least loaded at radio frequency, gives high quality at large volume and gives practically no intermodulation, due to the push-pull type of connection used. I

The circuits illustrated and described in detail will serve as examples. It will be obvious to supply any desired number of stages of amplification and to make alterations and introduce differences from the specific ar-c rangements shown. The invention is not, therefore, to be limited to the exact showing, including the numerical values that have been cited, but only by the scope of the claims.

VVha-t is claimed is: 1. In a receiving circuit an incoming circuit carrying a wide band of frequencies comprising the waves to be received, a pair of electric discharge devices having cathode, anode and grid or control electrodes, the cathodes and grids of the devices being connected in respectively opposite sense to said incoming circuit to impress said band upon each of said devices and a signal receiver differentially associated with the individual cathode-anode circuits of said devices through separate coupling-circuits having respectively different frequency-transmission characteristics, whereby said band of frequencies is transmitted to said signal receiver substantially without distortion;

2. In a selective amplification circuit for waves of a wide band of frequencies, two repeaters connected in differential relation to I a source of waves to be amplified, a load circuit for the reception of amplified wave energy, and output transformers of different frequency-amplitude transmission characteristic connecting said repeaters respectively to said load circuit, whereby substantially. uniform transmission for all frequencies in said band is'obtained.

8. A radio receiving circuit comprising a pair of electric discharge amplifiers connected in push-pull relation between an input circuit and an output circuit, means for sup 9lying radio Waves to said input circuit,a t ird electric discharge amplifier connected'to said I output circuit to receivethe amplified radio waves therefrom,a detector connected to the output of said third amplifier, connections from said detector for inipressinglthe detected low frequency waves upon t e input of said third amplifier, connections from the output of said amplifier to said input circuit for impressing the low frequency waves upfirst two amplifiers to the input of said third amplifier, the transformers having different frequency transmission characteristics so that together they transmita wide band of radio waves, a detector connected to the output of said third amplifier, connections from said detector for impressing the detected low fre- I quency waves on the input of said third amplifier, connections from the output of said amplifier to the input of the push-pull ampli fier circuit, and means responsive to the low frequency waves connected to the output of the push-pull amplifier circuit.

5. A radio receiving circuit comprising a source of waves representing a radio frequency wave modulated by a wide band of signal waves, a pair of electric discharge amplifiers, transformer means for impressing waves from said source differentially upon the inputs of said amplifiers, a third electric discharge amplifier, a pair of transformers of different frequency transmission character istics each having a primary winding connected to the output of one of said pair of amplifiers and a secondary winding connected to the input of said third amplifier a detector connected to the output of said third amplifier, means for connecting the output of said detector to the input of said third amplifier for impressing the detected signal frequency waves upon said third amplifier, a pair of transformers each responsive to signal frequency waves to the substantial exclusioniof radio frequency waves, one of said transformers having a primary winding connected to the output of said third amplifier and secondary windings connected to the input of said pair of'amplifiers for impressing the signal waves thereuponin difierential relation, the other of said transformers having a primary winding connected to the output of each of said pair of amplifiers and a secondmy name this 30th day of July, A. D. 1923.

DANA A. GRIFFIN. 

